Hydraulic speed governors

ABSTRACT

To counteract in a hydraulic governor for the effect of the decrease, at increased temperatures, in the flow that is delivered by a high-pressure displacement-type fuel pump upon the pressure drop produced by the flow in a metering orifice, temperature-responsive means are provided which at increased temperatures reduce the area of the metering orifice in proportion with the reduction in the volumetric efficiency of the pump that is due to the drop in viscosity of the hydraulic liquid at such higher temperatures.

United States Patent lnventor Appl. No.

Filed Patented Assignee Priority Robert S. Wood llford, England Dec. 22, 1969 Continuation of application Ser. No. 669,646, Sept. 21, 1967, now abandoned. Feb. 16, 1971 The Plessey Company Limited Sept. 23, 1966 Great Britain HYDRAULIC SPEED GOVERNORS 5 Claims, 3 Drawing Figs.

U.S. Cl 137/117, 137/26, 137/20 Int. Cl. G05d 27/00 Field ofSearch..... 137/117,

FUEL INLETI [56] References Cited UNITED STATES PATENTS 2,821,268 l/1958 Bourcier de Carbon 188/100 3,152,603 10/1964 137/117 3,204,623 9/1965 123/140 3,233,832 2/1966 239/155 3,332,436 7/1967 137/468 Primary Examiner-M. Cary Nelson Assistant Examiner-William H. Wright Attorney-Blum, Moscovitz, Friedman & Kaplan ABSTRACT: To counteract in a hydraulic governor for the effect of the decrease, at increased temperatures, in the flow that is delivered by a high-pressure displacement-type fuel pump upon the pressure drop produced by the flow in a metering orifice, temperature-responsive means are provided which at increased temperatures reduce the area of the metering orilice in proportion with the reduction in the volumetric efficiency of the pump that is due to the drop in viscosity of the hydraulic liquid at such higher temperatures.

I D -----m [IVE/Ni are hereinafter called hydraulic speed governors resulting pressure difference is generally applied to a control piston against the force of a loading spring, the resulting displace ment of the piston, from a normal position corresponding to the desired speed, being utilized to produce speed-correcting action. When the apparatus to be controlled is a combustion 1 engine having a displacement-type fuel pump, the cost and bulk of the governor could be reduced by utilizing the liquid delivered by the fuel pump to produce the speed-indicative pressure drop, but because of the high pressure against which a fuel pump nonnally operates and of the low rates of delivery occurring in fuel pumps, leakageof fuel in the pump constitutes in this case a considerable proportion of the total pump delivery, and this leakage increases considerably at higher temperature due to reduced viscosity of the fuel, so that at high temperatures the flow produced by the pump at a given speed is smaller than the flow produced at the same speed when the temperature is lower.

The present invention has for an object to provide automatic compensating means which counteract the influence of this decrease in the rate of effective delivery at rising temperatures upon the pressuredifference effecting the speed control. According to the present invention, in a fuel system in which a displaccment-type fuel pump delivers fuel to the engine against combustion pressure through a delivery line in which a metering orifice producing a pressure drop for the control of engine speed is arranged upstream of a variable-size spill aperture which deflects excess fuel away from the engine, the metering orifice is associated with temperature-responsive means which at increased temperatures decrease the effective area of the metering orifice in such manner as to maintain the pressure drop produced by the pump flow at a given speed substantially independent of the reduction in the volumetric efficiency of the pump with rising temperatures.

In a particularly simple form ofthe invention the metering orifice is constituted by an annular gap of short axial length formed between the piston on which the temperature drop acts and the bore of the cylinder in which the piston is movable, the automatic adjustment of the effective area of the orifice in accordance with temperature being achieved by constructing the piston of a material whose temperature expansion coefficient is higher by a suitable factor than that of the cylinder in which the piston is movable.

While ideally the whole delivery of the pump should pass through the metering orifice, a convenient possibility of adjusting the speed controlled by the governor can be afforded by providing a bypass controlled by an adjustable auxiliary orifice thus permitting a variable, but preferably small, portion of the total flow to bypass the metering aperture.

Two embodiments of the invention are illustrated in the accompanying drawings, in which:

FIG. I is a schematic sectional elevation showing one embodiment of the invention;

FIG. 2 similarly illustrates the preferred form of the invention; and v FIG. 3 is a fragmentary sectional elevation illustrating a modification.

Referring now first to FIG. 1, fuel from an inlet l is delivered by a gear-type fuel pump a driven by an engine whose speed is to be controlled, at a rate which apart from leakage losses, is proportional to the speed of the engine, and the liquid fuel delivered by the pump a is passed through a metering orifice b to a fuel line D leading to the engine. The passage of the fuel through the orifice b produces a pressure drop which is substantially proportional to the square of the rate of flow, and

thus, approximately of the engine speed; the resultant pressure difference is applied to a piston c movable in a cylinder 3 in which the action of the pressure downstream of the orifice b upon the piston c is assisted by a loading spring d so as to balance the piston in the illustrated position when the engine speed is somewhat below the desired speed. When the desired speed is reached, the piston is displaced to the right of the FIG., thus causing a slide valve element k movable with the piston cto allow a certain amount of fuel to spill back from the delivery line d to a return line e leading back to the fuel in the inlet I. If the engine speed rises above the normal speed, the amount of fuel allowed to spill back is increased, thus causing less fuel to reach the engine, whose speed will therefore decrease. When on the other hand the speed of the engine drops below the normal value, less fuel is allowed to spill back, thus increasing the amount of fuel reaching the engine and thus the power of the engine; and this increased fuel supply will cause the engine speed to increase.

It will be appreciated, however, that at higher temperatures the delivery of the pump at a given speed will decrease due to reduction in the viscosity of the fuel, which results in an increase in leakage losses of the pump a, the and in order to compensate for the resulting decrease in the pressure drop in the orifice b, is provided with a needle-type plunger 1' carried by a temperature-sensitive element f which, its temperature increases, moves the plug i towards the orifice b, thereby reducing the effective area of the orifice at the same rate at which the increased leakage losses of the pump reduce the flow through the orifice at a given engine speed. The engine speed may be set to a desired value within certain limits by manually adjusting a further plug 1 to vary the size of an auxiliary orifice h which is connected in parallel to orifice b, and whose area is small compared with the area of the orifice b.

FIG. 2, in which parts corresponding to those of FIG. 1 are indicated by the same references supplemented by an apostrophe if the part is modified, illustrates a simplified arrangement in which a metering aperture is constituted by an annular gap b formed between the edge of the control piston c' and the cylinder e in which this piston operates, the piston c" being narrowed in knife-edge fashion towards its circumference and being made of a material whose coefficient of thermal expansion is greater than that of the cylinder g in such manner that with increase in temperature the gap b will decrease in width according as the leakage losses of the pump increase.

FIG. 3 illustrates a modification of this construction, which reduces the risk'of the creation of instability by high-velocity flow past the control piston c of FIG. 2.

With this object in view a baffle plate 2, having less clearance from the wall of the cylinder g than the piston c is arranged to be passed by the flow downstream of the gap b to block the path of the direct high velocity flow from the gap b. The illustrated baffle z has a number of holes in for the passage of the metering flow, but alternatively all the mete ring flow may be arranged to flow past the outer edge of the baffle. The amount of clearance n at this edge is not critical but should be smaller than the clearance :round the piston 0.

While the invention has been described as applied to hydraulic governors operated by the delivery of a fuel pump in a combustion engine, the invention is not limited to this particular use but can be applied whenever the effect of variation due to temperature influences in the delivery of a displacement pump employed to produce a flow through a metering orifice is to be reduced.

Iclaim:

l. A combined fuel-supply and speed-governor system for a combustion engine, comprising in combination a displacement-type fuel pump adapted to be driven by such engine at a speed proportional to engine speed and delivery fuel to such engine against combustion pressure, a delivery line leading from the pump to the engine and including a metering orifice, a variable-size spill aperture in said line downstream of said orifice for diverting from the engine part of the fuel delivered by the pump, engine-speed control means responsive to the pressure drop developed in said orifice by the fuel flow and operative to vary the size of said spill aperture, and means responsive to the temperature of the fuel delivered by the pump to decrease the size of said orifice in response to an increase of the fuel temperature at such a ratio as to substantially compensate for the reduction in the volumetric efficiency of the pump due to the decrease of fuel viscosity with rising temperature.

2. A system as claimed in claim 1, wherein said means responsive to the pressure drop in said orifice include a cylinder and a piston movable in said cylinder, the metering orifice being constituted by an annular gap of short axial length between said piston and cylinder, and said piston being made of a material whose temperature expansion coefficient is higher than that of the cylinder.

3. A system as claimed in claim 2, including a baffle movable with the piston and moving jointly with the piston and extending into the path of fuel flow from said annular gap to dissipate part of the kinetic energy of the fuel flowing through said gap. I

4. A system as claimed in claim 1, wherein said means responsive to the fuel temperature include a needle-type plunger extending axially into said orifice and a temperaturesensitive element attached to said plunger and operative to vary its depth of penetration into the orifice in accordance with the temperature of the liquid passing through the orifice.

5. A system as claimed in claim 1, wherein the delivery line is provided with a branch bypassing said orifice, the system including in said branch a throttle orifice of a size small in comparison to the size of said metering orifice, and means for adjusting the size of said throttle orifice. 

1. A combined fuel-supply and speed-governor system for a combustion engine, comprising in combination a displacement-type fuel pump adapted to be driven by such engine at a speed proportional to engine speed and delivery fuel to such engine against combustion pressure, a delivery line leading from the pump to the engine and including a metering orifice, a variablesize spill aperture in said line downstream of said orifice for diverting from the engine part of the fuel delivered by the pump, engine-speed control means responsive to the pressure drop developed in said orifice by the fuel flow and operative to vary the size of said spill aperture, and means responsive to the temperature of the fuel delivered by the pump to decrease the size of said orifice in response to an increase of the fuel temperature at such a ratio as to substantially compensate for the reduction in the volumetric efficiency of the pump due to the decrease of fuel viscosity with rising temperature.
 2. A system as claimed in claim 1, wherein said means responsive to the pressure drop in said orifice include a cylinder and a piston movable in said cylinder, the metering orifice being constituted by an annular gap of short axial length between said piston and cylinder, and said piston being made of a material whose temperature expansion coefficient is higher than that of the cylinder.
 3. A system as claimed in claim 2, including a baffle movable with the piston and moving jointly with the piston and extending into the path of fuel flow from said annular gap to dissipate part of the kinetic energy of the fuel flowing through said gap.
 4. A system as claimed in claim 1, wherein said means responsive to the fuel temperature include a needle-type plunger extending axially into said orifice and a temperature-sensitive element attached to said plunger and operative to vary its depth of penetration into the orifice in accordance with the temperature of the liquid passing through the orifice.
 5. A system as claimed in claim 1, wherein the delivery line is provided with a branch bypassing said orifice, the system including in said branch a throttle orifice of a size small in comparison to the size of said metering orifice, and means for adjusting the size of said throttle orifice. 